netdev - Re: [PATCH net] r8169: disable TSO on a single version of RTL8168c to fix performance

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Date:   Tue, 19 Nov 2019 16:42:57 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     vinschen@...hat.com
Cc:     netdev@...r.kernel.org, hkallweit1@...il.com, nic_swsd@...ltek.com
Subject: Re: [PATCH net] r8169: disable TSO on a single version of RTL8168c
 to fix performance

From: Corinna Vinschen <vinschen@...hat.com>
Date: Tue, 19 Nov 2019 10:09:39 +0100

> During performance testing, I found that one of my r8169 NICs suffered
> a major performance loss, a 8168c model.
> 
> Running netperf's TCP_STREAM test didn't return the expected
> throughput of > 900 Mb/s, but rather only about 22 Mb/s.  Strange
> enough, running the TCP_MAERTS and UDP_STREAM tests all returned with
> throughput > 900 Mb/s, as did TCP_STREAM with the other r8169 NICs I can
> test (either one of 8169s, 8168e, 8168f).
> 
> Bisecting turned up commit 93681cd7d94f83903cb3f0f95433d10c28a7e9a5,
> "r8169: enable HW csum and TSO" as the culprit.
> 
> I added my 8168c version, RTL_GIGA_MAC_VER_22, to the code
> special-casing the 8168evl as per the patch below.  This fixed the
> performance problem for me.
> 
> Fixes: 93681cd7d94f ("r8169: enable HW csum and TSO")
> Signed-off-by: Corinna Vinschen <vinschen@...hat.com>

Applied, but it would be really nice to know why this is happening
instead of just turning it off completely.